Staple fibers for blends

ABSTRACT

A process for making a yarn from a blend of staple fibers including at least some drawn polyethylene terephthalate fibers and at least some underdrawn higher shrinkage polyethylene terephthalate fibers, in which the underdrawn polyethylene terephthalate fibers have a length significantly shorter than the effective staple length of the blend. This process overcomes difficulties in spinning blends of staple fibers containing e.g., high shrinkage synthetic underdrawn polyethylene terephthalate fibers, particularly when the spinning is done on the cotton system and when nips of the feed and draft rollers in the spinning unit are spaced apart by a distance just above the effective staple fiber length of the blend.

United States Patent Thomson 1451 Aug. 29, 1972 [73] Assignee: Imperial Chemical Industries,

Limited, London, England [22] Filed: Dec. 15, 1970 [21] Appl. No.: 98,456

[30] Foreign Application Priority Data Dec. 19, 1969 Great Britain ..62,009/69 [52] US. Cl .1. ..57/157 R, 57l55.5, 57/ 140 BY [51] Int. Cl. ..D02g 3/24 [58] Field of Search .57/55.5, 140 R, 140 BY,157 R, 57/157 S, 157 MS; 28/72.l7; 264/168, 210,

3,388,547 6/ 1968 Koga et a1 ..57/ 140 X 3,438,192 4/1969 Ryan,Jr. ..57/140 3,587,220 6/1971 Eggleston ..57/l40 Primary Examiner-Wemer H. Schroeder Attomey-Cushman, Darby 8L Cushman ABSTRACT A process for making a yarn from a blend of staple fibers including at least some drawn polyethylene terephthalate fibers and at least some underdrawn higher shrinkage polyethylene terephthalate fibers, in which the underdrawn polyethylene terephthalate fibers have a length significantly shorter than the effective staple length of the blend. This process overcomes difficulties in spinning blends of staple fibers containing e.g., high shrinkage synthetic underdrawn polyethylene terephthalate fibers, particularly when the spinning is done on the cotton system and when nips of the feed and draft rollers in the spinning unit are spaced apart by a distance just above the effective staple fiber length of the blend.

6 Claims, No Drawings STAPLE FIBERS FOR BLENDS This invention relates to staple fibers for blends and to an improved process for making polyester yarns. More particularly it relates to the manufacture of yarns from blends comprising high and low shrinkage polyester fibers.

Blends of staple fiber containing high shrinkage synthetic under-drawn polyethylene terephthalate fibers having a shrinkage of about 30 percent in boiling water, and of low or normal shrinkage synthetic fibers, having a shrinkage of about 6 percent in boiling water, are known. Blends of such high and normal shrinkage synthetic fibers with other fibers including man-made and natural fibers are also known.

Difficulties are experienced however when spinning such blends containing high shrinkage synthetic fibers particularly on the cotton system and when nips of the feed and draft rollers in the spinning unit are spaced apart by a distance just above the effective staple fiber length of the blend; for instance 54 mm for an effective staple fiber length of 50 mm.

Drafting ratios as high as 20:1 or 40:1 are used between rollers spaced apart by a distance only slightly greater than the effective staple length of the blend. We have found that under such circumstances inter-fiber drafting forces are sufficient to stretch under-drawn fibers far enough to impair their high shrinkage properties and even to cause over-length fibers which may be gripped simultaneously by both feeding and drafting rollers. These difficulties are most serious on the cotton spinning system where the fibers are not supported in the drafting zone between feeding and drafting rollers, and to retain adequate fiber control in the drafting zone the rollers are spaced apart by a distance only slightly greater than the effective staple fiber length. We have however found that some loss of control of underdrawn high shrinkage fibers can readily be accepted during drafting of such blends, because in subsequent yarn or fabric treatment these fibers tend to shrink towards the core of the yarn leaving the yarn surface rich in lower shrinkage fibers.

According to this invention we therefore provide a process for making a yarn from a blend of staple fibers including at least some drawn polyethylene terephthalate fibers and at least some underdrawn higher shrinkage polyethylene terephthalate fibers, in which the underdrawn polyethylene terephthalate fibers have a length significantly shorter than the effective staple length of the blend.

The length of the high shrinkage fibers should not exceed 90 percent preferably 60-80 percent of the effective or nominal fiber length of the blend.

In practice we have found that in this way the high shrinkage synthetic fibers will not be cold-drawn to exceed the nominal or effective fiber length. When our high shrinkage fibers are shorter than the nominal fiber length and less than the standard setting between drafting rollers, difficulties due to cold drawing of these fibers between the rollers and resulting overlengths are avoided.

The high shrinkage underdrawn poly(ethylene terephthalate) fibers display a low crystallinity, low modulus and low yield stress, compared with normal commercially available staple fiber, such as polyester including poly(ethylene terephthalate) and viscose staple fibers. The underdrawn high shrinkage fibers can be elongated up to about 100 percent of their initial length; and they may break under a load of about 7g. However the initial elongation requires comparatively low loads, and we believe that because of this, the formation of overlength" fibers is engendered unless precautions are taken so that they are not gripped during processing, such as drafting, by cutting them to a shorter effective length.

By cutting the high shrinkage fibers to shorter lengths than the effective length, we believe that the so cut shorter fibers are carried by the other fibers and they do not become elongated even on drafting systems using spaced positive nips, such as the drafting rolls on a cotton spinning system.

Suitable proportions of high shrinkage fibers in a blend are about 20 percent and up to 50 percent preferably 25 percent. The proportion of drawn poly(ethylene terephthalate) fibers may be about 25 percent preferably 50 percent and up to percent. The blend may also contain other fibers, particularly cellulose fibers such as viscose fibers, in a proportion of about 25 percent and up to about 50 percent.

The following tables A and B illustrate typical blends which have been processed on the cotton system without difficulty and which resulted in strong uniform yarns.

TABLE A 25% high 3.3d. tex poly( ethylene terephthalate) 38 mm. shrinkage fiber 50% normal 3.3d. tex poly( ethylene terephthalate) 50 mm.

fiber 25% normal 3.3d. tex Viscose fiber 50 mm.

TABLE B 25% high 3.3d. tex poly(ethylene terephthalate) 38 mm. shrinkage fiber 50% low 3.3d. tex poly(ethylene terephthalate) 50 mm. l.V. low fiber pilling 25% normal 3.3d. tex Viscose fiber 50 mm.

The following examples in which all parts and per-, centages are by weight, illustrate but do not limit our invention.

EXAMPLE 1 A blend of staple fibers as set out in Table A was prepared. The poly(ethylene terephthalate) high shrinkage fibers are commercially available as TERYLENE (Regd. Trade Mark) M30, Type 755, the normal poly(ethylene terephthalate) fibers are available as TERYLENE M 16 series 5 2 and the Viscose staple fibers as SARILLE (Regd. Trade Mark).

When these fibers are processed on the cotton system, including carding and spinning, satisfactory uniform yarns are produced. TERYLENE Type 755 is a melt-colored staple fiber which is capable of being subjected to heat-shrinkage during the fabric finishing stage. The fiber is sensitive to high temperatures and it is therefore imperative that it is not exposed to temperatures above 50C before the fabric finishing stage in order to preserve the high shrinkage characteristics, which in the blend results in a bulkier yarn and a fabric with a fuller handle, greater cover and softer, loftier feel than a cotton type fabric. The finished fabric is comparable with a worsted type fabric.

During the heat treatment relaxation stage at about 70C in fabric finishing the high-shrinkage fiber component of the blended yarn migrates to the core of the yarn during the relaxation stage and a color change may occur, the extent or" which will depend on the color contrast between the high shrink component and the other fibers. A fabric shrinkage of about 13 percent will occur, compared with only percent if no high shrink fibers are present.

Fabrics produced from these yarns containing our high shrinkage fiber have many applications including high quality suiting fabrics which can thus be produced with considerable saving in time and cost, when using the efficient and cheapercotton spinning system, in which the shorter high-shrunk fiber is designed to enable this fiber to be carried by other fiber components in the blend without undue stretching between drafting rollers.

EXAMPLE 2 A blend of staple fibers set out in Table B was prepared, in which the high shrinkage fiber component is as described in Example 1. The low pilling poly(ethylene terephthalate fiber) is commercially available as TERYLENE Type 552 which has a low intrinsic viscosity of 0.40.

The blend is processed on the cotton system including opening carding and spinning and satisfactory uniform yarns are produced. Fabrics from these yarns can be woven from doubled yarns. Because of the low pilling poly(ethylene terephthalate) fiber component, the fabric will not give rise to undue pilling during normal processing and wear.

The underdrawn high shrinkage poly(ethylene terephthalate) fibers are produced from meltspun filaments having a birefringence corresponding to 4.10", by drawing a tow of such filaments in water at 75C, at a draw ratio of 2.56:1, followed by crimping in a'stuffer box crimper, drying below 50C and cutting to 38 mm. staple lengths.

COMPARATIVE EXAMPLE 3 Example 1 is repeated except that the high'shrinkage poly( ethylene terephthalate) fibers have a length of 50 mm. At processing through the cotton spinning system using conventional drafting and setting conditions, excessive numbers of overlength fibers are formed which inhibit processing and which result in faulty and irregular yarn.

An attempt was then made to improve performance by widening settings between the drafting rollers but they can therefore be accommodated. Because of the I shorter length of the high shrinkage fibers, they do not come under high tension and they remain well clear of the first nip point before being taken up by the next nip li iivill be appreciated that the short high shrinkage underdrawn poly(ethylene terephthalate) fibers should not be processed in 100 percent form but that they should be carried by other longer fibers, which may be achieved by blending in appropriate proportions at the opening stage.

What we claim is:

ll. A process for producing a yarn from a blend of staple fibers comprising the steps of (a) blending drawn poly(ethylene terephthalate) fibers with underdrawn, higher-shrinkage poly( ethylene terephthalatc) fibers, said underdrawn higher-shrinkage fibers having lengths no greater than about 90 percent of the effective fiber length of the staple fiber blend; and (is) spinning the staple fiber blend so produced with a drafting system with positive nips set and spaced just above said effective fiber length of the staple fiber blend.

2. The process of claim ll, wherein said yarn is spun on the short staple spinning system.

3. The process of claim ll, wherein from about 20 to about 50 percent (by weight) of said staple fiber blend is comprised of underdrawn higher-shrinkage poly(ethylene terephthalate) fibers with lengths no greater than from about 60 to about 80 percent of the effective fiber length of the staple fiber blend.

The process of claim 3, wherein said staple fiber blend is comprised of from about 25 to about percent (by weight) of said drawn poly(ethylene terephthalate) fibers.

5. The process of claim 4, wherein said staple fiber blend is comprised of about 25 weight percent of said underdrawn higher-shrinkage poly(ethylene terephthalate) fibers and about 50 weight percent of said drawn poly(ethylene terephthalate) fibers.

6. The process of claim 3, wherein said staple fiber blend is comprised of from about 25 to about 50 weight percent of Viscose staple fibers. 

2. The process of claim 1, wherein said yarn is spun on the short staple spinning system.
 3. The process of claim 1, wherein from about 20 to about 50 percent (by weight) of said staple fiber blend is comprised of underdrawn higher-shrinkage poly(ethylene terephthalate) fibers with lengths no greater than from about 60 to about 80 percent of the effective fiber length of the staple fiber blend.
 4. The process of claim 3, wherein said staple fiber blend is comprised of from about 25 to about 75 percent (by weight) of said drawn poly(ethylene terephthalate) fibers.
 5. The process of claim 4, wherein said staple fiber blend is comprised of about 25 weight percent of said underdrawn higher-shrinkage poly(ethylene terephthalate) fibers and about 50 weight percent of said drawn poly(ethylene terephthalate) fibers.
 6. The process of claim 3, wherein said staple fiber blend is comprised of from about 25 to about 50 weight percent of Viscose staple fibers. 